1. Field of the Invention
This invention relates to a control system for a vehicle provided with an automatic transmission having a lockup mechanism.
2. Description of the Prior Art
As disclosed, for instance, in Japanese Unexamined Patent Publication No. 60(1985)-1464, there has been known a control system for a vehicle provided with an automatic transmission having a lockup mechanism in which fuel to be supplied to the engine is cut and at the same time the lockup mechanism is caused to engage with a controlled engaging force when the engine is being decelerated, and the lockup mechanism is subsequently caused to disengage when the deceleration of the engine finishes and fuel supply to the engine is resumed so that fluctuation in the engine torque generated upon resumption of fuel supply is absorbed by the torque converter and the torque shock generated due to the fluctuation in the engine torque is suppressed.
However it has been found that, if the automatic transmission downshifts during deceleration of the engine, the conventional control system can determine that deceleration of the engine has finished though the engine is still decelerating since the automatic transmission once shifts to neutral before shifting to the target gear speed and the engine speed temporarily falls by a large amount while the automatic transmission is in neutral. As a result, the lockup mechanism is caused to disengage though the engine is still decelerating and even if the engine speed is increased again in response to completion of the downshift, the lockup mechanism cannot be engaged again before the deceleration of the engine finishes since it takes a certain time to establish a control hydraulic pressure necessary for causing the lockup mechanism to engage.